Sleep cycles linked to health

Yalies who stay up late studying for their midterms may be weakening their immune systems.

A new study published Feb. 16 in the journal Immunity has revealed a relationship between circadian rhythms and immune system activity in mice. According to Erol Fikrig, Yale professor of epidemiology and microbial pathogenesis and the lead author of the study, this finding demonstrates the importance of keeping regular sleep cycles to stay healthy. It also has implications for making vaccinations more effective, he said.

“We’ve known for quite some time that people intuitively say they get sicker when they’ve had jet lag and poor sleep,” Fikrig said.

He said the study was important because it was the first to specifically link circadian rhythms with the expression of Toll-like receptor 9 (TLR-9), a protein involved in immune function in mice. The gene for TLR-9 was expressed in varying degrees depending on the time of day, with the highest levels found while the mice were active, he said. The research showed that when mice were exposed to an infection, the “outcome” varied depending upon the time of day of the exposure.

While he stressed that the study has not yet been conducted in humans, Fikrig posited that sleep-cycle disruption might weaken human immune systems. He said when an individual’s circadian rhythms are “out of whack,” gene expression for certain immune proteins might be suppressed.

The study may lead hospitals to reconsider certain standard practices that disregard the importance of sleep, Fikrig said. For example, nurses often wake patients up in the middle of the night for checkups, but this practice could be deleterious to patients’ immune systems.

The study also examined the effectiveness of vaccination at different times of day. Responses to vaccines in mice varied with the time of day they received the vaccines, indicating, Fikrig said, that there could be an optimal time of day for humans to be vaccinated.

Brian Abaluck ’01, a sleep specialist at Sleep HealthCenters — a health care provider specializing in sleep medicine — cautioned that it was “dicey” to extrapolate animal studies to humans.

“[I] would not change my recommendations to patients based on a single mouse study,” Abaluck said.

Nonetheless, he said studies like this one add to general knowledge about sleep and health.

Abaluck said the study is consistent with his understanding of sleep health, since previous studies have shown that sleep deprived mice eventually die from “overwhelming infection.” Other studies have shown that people who do not get adequate sleep tend to get sick more and benefit less from vaccinations, he said.

Abaluck added that the relationship between sleep and learning is as clear as that between sleep and health. For example, he said, people perform much worse on cognitive tasks after sleeping for only one hour — and they also feel “awful.” But although people reach a sleep plateau after getting five to six hours of sleep per night for a week and no longer feel sleepy, their performance on cognitive tasks is just as impaired as after only an hour of sleep.

“If I could go back to college, I would prioritize sleep more,” Abaluck said. “I would try to keep as regular a sleep time as possible — even on the weekends.”

Fikrig also joked that students should think twice about studying into the wee hours if they want to stay healthy.

Ran Matsumoto ’14 said she is not surprised to hear that immune function and sleep might be linked, since she always feels worse after not getting enough sleep.

“I feel that a lot of the time [Yale students] put academics before sleep,” Matsumoto said.

A spring 2011 survey by the News found that the Yalies said they average 6.4 hours of sleep per night.